1. Field of the Invention
This invention relates to the methods of forming copper-based interconnections such as trenches, via holes, contacts and thin films in the submicron class of semiconductor technology areas by means of chemical vapor deposition(CVD) method using catalyst.
2. Description of the Related Art
Interconnecting active and passive elements as well as providing signal and power lines have been playing a vital role in the semiconductor-related product manufacturing processes.
Most widely used method is to use aluminum-based metals by means of deposition, etching, etc. because aluminum alloys are relatively easy to handle for processing, easy to obtain and inexpensive. However, aluminum alloys are known to be weak under high electrical as well as thermal stresses, causing a failure mechanism know as electromigration problem primarily due to the grain size.
Furthermore, as the device designrule becomes tighter, the grain size of aluminum alloys becomes more serious concern because of the aforementioned electromigration-related problems. Aluminum alloys are generally known as good conductors, thereby meeting the interconnection requirements including electrical performance requirements, such as RC time delays.
Recently, as the circuit density increases rapidly, high performance devices in terms of short time delays and better conductivity as well as robust physical characteristics of the interconnecting conductors with less electromigration problem is becoming increasingly desirable. As a result, better conductive materials, particularly, copper materials to replace aluminum alloys have been actively studied.
Since copper has high conductivity, it has advantages, among which copper is able to carry more currents while the electromigration-related problems are much less and also copper is very robust compared to aluminum. On the other hand, copper is significantly harder than aluminum, thereby it is difficult to etch compared to aluminum alloys, for which xe2x80x9cdeposit-and-then-etchxe2x80x9d process can be readily applied. Therefore, in order to form an interconnecting conductor, for example, a damascene process is used, where a trench is formed on an insulating layer by means of etching and then the trench is filled with copper. Furthermore, in order to connect two conductors in two different layers, one on top of the other, via holes or contact holes are used. In this case, a dual damascene process, where the two steps of trenches and via holes or contact holes in two adjacent layers, one on top of the other, are filled with copper in one process step, may be used.
A widely used technology for filling trenches and holes is electroplating(EP) method. However, this process does not conform very well and also is not compatible well with the conventional semiconductor processing steps. Also, this process is rather complex and needs to be developed further in order to achieve high yield in a mass-production environment. For a good compatibility or conformity with conventional semiconductor device manufacturing processes, use of chemical vapor deposition(CVD) or physical vapor deposition(PVD) method such as sputtering technique is desirable. When sputtering technique is used to form interconnecting conductors using trenches and holes, a pinch-off phenomenon occurs near the top opening area of a deep trench or a deep hole. That is, the opening at the top is plugged up before the rest of the trench or the hole is filled. This is caused by the unique nature of xe2x80x9cdirectxe2x80x9d deposition along the xe2x80x9cline of sightxe2x80x9d occurring generally during a PVD process. This is why the sputtering technique is not best suited yet for submicron class of semiconductor device manufacturing.
On the other hand, it is known that use of a chemical vapor deposition(CVD) method makes it possible to nucleate thin films and also to grow the thin films. It is also known that a CVD method provides a good step coverage, thereby the deposited film or a thin layer covers the flat parts(flat part at the top and bottom), the walls as well as the comers reasonably well. It has been reported, however, that when copper material is deposited by means of a CVD at about 200xc2x0 C. of the substrate temperature, not only the film growth rate decreases below 50 nm/minute, which is considered as a slow rate, but also the film surface becomes bumpy, because the thin film after its nucleation starts growing like islands at the beginning of the growth.
In order to solve aforementioned problem of rather slow growth rate of a thin film and the bumpiness of the surface of the thin film when a CVD method is used for forming a thin film, a chemical deposition method using catalyst on the surface has been proposed and disclosed in the U.S. patent application Ser. No. 09/554,444 by Lee, where the proposed chemical vapor deposition method suggests use of iodine or bromine, which are members of halogen family of elements, as a catalyst in conjunction with a CVD. This method not only increases the growth rate of the copper film significantly, but also reduces the bumpiness of the resultant film surface.
The present invention proposes methods of forming copper interconnecting conductors such as trenches, via holes, contacts and thin films by means of chemical vapor deposition(CVD) method using catalysts as described in the following.
A method of forming copper interconnecting conductors by filling trenches, via holes and contacts without creating pinch-offs and voids by means of copper chemical vapor deposition(copper CVD) using catalyst is disclosed and presented. In a first aspect of the present invention, a method of using iodine or bromine as a catalyst in conjunction with a copper CVD method in filling trenches, via holes and contacts without creating undesirable pinch-offs and voids is disclosed and presented. This method fills the bottom part of the trenches and holes very fast without creating pinch-offs and voids, and the rate of deposition decreases as the trenches and holes are filled from bottom up, and copper is deposited at the slowest rate at the top surface. Unlike the conventional method such as a PVD method, the method of copper CVD using catalyst does not create pinch-offs at the top openings of trenches and holes.
In a second aspect of the invention, a method of forming a copper layer in narrow and deep trenches and small in diameter and deep holes by repeatedly applying the method described in the first aspect of the present invention is disclosed and presented. This method allows copper material deep into trenches and holes, thereby the deep trenches and holes can be filled with copper, while the conventional method such as sputtering technique would not allow such deep penetrations.
In a third aspect of the invention, a method of forming a very thin copper layer at the top surface is disclosed and presented, thereby the thin copper layer can be removed by etchback means, in preparation for the subsequent steps of processing, whereas this removal is typically carried out by rather expensive chemical mechanical polishing(CMP) method. Normally, conventional electroplating technique requires CMP method for removal of the copper at the top surface in preparation for the subsequent steps in processing.